Medical electrode with relatively rigid electrolyte cup

ABSTRACT

An electrode for attachment to the skin is made from an adhesively coated, elastic sheet sandwiched between a nonconducting, low profile cup member and a clamp plate fixed in assembled relation by a conductive snap fastener member extending therethrough. Both the cup member and the clamp plate are in the form of cavity washers, the confronting margins of which squeeze the sheet. In use, the cup member cooperates with the skin to form an enclosed cavity for an electrolyte. When pressed against the skin, the elastic sheet resiliently urges the cup member against the skin.

United States Patent Szpur Oct. 10, 1972 [54] MEDICAL ELECTRODE WITHRELATIVELY RIGID ELECTROLYTE CUP [72] Inventor: Roman Szpur, Dayton,Ohio [73] Assignee: MDM Corporation, Dayton, Ohio [22] Filed: Feb. 13,1970 [21] Appl. No.: 11,208

[52] US. Cl. ..128/2.l E, 128/D1G. 4

[51] Int. Cl. ..A61b 5/04 [58] Field of Search ..128/2.06 E, 2.1 F, 404,417, l28/DlG. 4

[56] I References Cited UNITED STATES PATENTS 2,632,447 3/1953 Dobes....128/404 2,651,304 9/1953 Browner 128/417 3,187,745 6/1965 Baum et211. 128/2.06E

3,085,577 4/1963 Berman et a] ..128/2.06 E 3,340,868 9/1967 Darling..128/2.06 E 3,380,445 4/1968 Fraslcr ..128/2.06 E

Primary Examiner-William E. Kamm Attorney-H. Talman Dybvig [5 7]ABSTRACT 17 Claims, 4 Drawing Figures PATENTEDnm 10 I972 3.696, 807

INVENTOR. BUM/IN SZPUE MEDICAL ELECTRODE WITH RELATIVELY RIGIDELECTROLYTE CUP BACKGROUND OF THE INVENTION This invention relates tomedical electrodes of the type used to detect electrical signals fromthe skin of a living subject and more particularly to the type of suchelectrode which is designed for use over several days withoutinterfering with the subjects normal activities.

The electrode of this invention is designed for use with commerciallyavailable electrolytes in the form of electrode pastes or gels. It isknown that the conductor portions of such electrodes should be spacedfrom the skin of the subject by the electrolyte to obtain the leastresistance and to minimize motion artifacts or noise.

. Optimum results are obtained when the volume of electrolyte and itsareas of contact over the skin nd the conductor portion of the electroderemain constant.

Electrodes have been made with barriers to prevent contact between theskin and their conductor portions. The barriers are provided with smallapertures to be filled with an electrolyte. Although such devices mayminimize artifacts, they are difficult and thus costly to construct, andthe imposition of the apertured barrier undesirably reduces conductionbetween the skin and the conductor portion of the electrode.

Other electrodes have been made without any barrier between the skin andthe electrode conductor. For the most part these have been designed toprovide electrical contact with only a very small skin area. One type ofelectrode provides for contact over a relatively large skin area. Toobtain the necessary isolation between the metal conductor and the skin,these electrodes have a relatively high profile, that is, a large heightto diameter ratio. However, low profile electrodes are preferred tominimize the possibility of movement of the electrolyte, which may causespurious signals, and to minimize the inconvenience experienced by thesubjects wearing the electrodes.

SUMMARY OF THE INVENTION F The electrode of this invention is providedwith a relatively rigid, non-conductive, low profile cup member having aconvexly curved rim and placed in an inverted position on the skin ofthe subject. The cup member is effectively clamped to the skin by anoverlying elastic sheet having a pressure sensitive adhesive surroundingthe cup member. When attached to the skin, the elastic sheet resilientlypresses the cup member against the skin to firmly hold the cup member ina fixed position. Separation of the elastic sheet from the cup member isprevented by a clamp plate positioned on top of the sheet. The conductorportion of the electrode includes a thin conductive plate located in thecavity between the cup member and the skin, the conductive plateabutting the base of the cup member. The entire cup member can be filledwith an electrolyte to provide a broad. area of contact over theskin.

For simplicity of construction, the conductor comprises a snap fastenermember projecting through the cup member, the carrier sheet and theclamp plate to hold these parts in assembled relation. Also, the clampplate is preferably constructed identically to the cup member, bothbeing similar to cavity washers. The confronting margins of the cupmember and the clamp plate squeeze an annular projection of the elasticsheet thereby to assist in holding the center portion of the elasticsheet under tension when the lower surface of the elastic sheet isadhered to the skin.

The elastic sheet is desirably a sponge like material, preferably opencell polyvinylchloride, because such material may be stretched in alldirections and has an elastic character. When using open cellpolyvinylchloride sheet or the like it is desired that both the upperand lower surfaces have a relatively closed cell construction. Apartially closed cell construction is desired on the lower surface tobetter form a barrier layer for receiving a pressure sensitive adhesive.The top surface is preferably closed cell because closed cell surfacesdo not retain dirt as readily as open cell material. The relativelyclosed cell surfaces also contribute to the elasticity of the sheetwhich is necessary to maintain the cup member pressed against the skin.A sheet made from open cell polyvinylchloride with partially closed cellupper and lower surfaces also has the advantages of being inexpensive,soft to the touch and pleasing in appearance. Air readily passes throughsuch material to ventilate the skin. When an electrode in accordancewith this invention is adhered to the skin, even for extended periods ofuse, substantially the only sensation experienced by the subject is thetackiness of the adhesive.

Generally stated, it is an object of this invention to provide animproved, low-profile, inexpensive medical electrode and especially onefor use over extended periods of time. Other objects and advantages willbecome apparent from the drawing and the following description.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of anelectrode made in accordance with this invention shown applied to thehand of a subject;

FIG. 2 is a cross sectional view of the electrode, taken along line 2-2of FIG. 1, applied to the skin;

FIG. 3 is an exploded perspective view of an electrode in accordancewith this invention and a protective sheet for the adhesive prior toassembly of these parts; and

FIG. 4 is a cross sectional view of an electrode made in accordance withthis invention with a different type of protective member.

DESCRIPTION OF THE PREFERRED EMBODIMENT An electrode generallydesignated 10 made in accordance with this invention is shown secured tothe hand H of a subject in FIGS. 1 and 2. The electrode 10 consists of acircular, elastic pad or sheet 12 overlying a centrally located,inverted cup member 14, a clamp plate l6 located on top of the sheet 12in alignment with the inverted cup member 14, and a metallic conductorformed from a male snap fastener member, generally designated 18. Theannular area of the lower surface of the sheet 12 in surroundingrelation to the cup member 14 is provided with a pressure sensitiveadhesive layer 20 for attachment of the electrode 10 to the skin. Inuse, electrical signals from the skin are amplified and sensed byapparatus (not shown) connected to the snap fastener member 18 by aconductive lead and cooperating snap fastener member, shown by phantomlines 18a. The electrical path is from the skin through an electrolyteconfined in a chamber or cavity 42 enclosed by the cup member 14 and theskin, and thence throughthe snap fastener member 18.

With reference to FIGS. 2 and 3, the cup member 14 is in the form of acavity washer and has a circular flat base 22 surrounded by an annularflange 24 which is semicircular or U-shaped in cross section. The centerof the cup base 22 is apertured as indicated'at 26. The cup member 14 iselectrically non-conductive and can be vacuum formed from a relativelythin sheet of a suitable thermoplastic. such as vinyl, linearpolyethylene, cellulose acetate butyrate, or the like.

The clamp plate 16 is also non-conductive and is preferably identicallyconstructed to the cup member 14 and accordingly includes a circularflat base 28 .with a U-shapedrim or flange 30 and has a central aperture32. As will become apparent, the shape of the clampv plate 16 is notcritical but the shape illustrated is preferred because of the savingsin manufacturing costs resulting from use of the same parts for both thecu member 14 and the clamp plate 16.

The. male snap fastener member .18 comprises a lower circular plateportion. 34 from the center of which a hollow, open ended stud 36 isformed upwardly, and an upper plate 'portion- 38 having an upwardlyprotruding, hollowsocket 40. To assemble the parts forming the electrode10, the cup member 14 and the clamp plate 16 are first centrally locatedand aligned on opposite sides of the sheet 12. The stud 36 is theninserted throughthe aperture 26, pierced through the center of the sheet12 and then through the aperture 32 into the socket 40. The parts of thesnap fastener member 18 are then pressed together whereupen the upperend of the stud 36 folds inwardly and its side walls collapsesoutwardly, causing the fastener member parts to be tightly wedgedtogether. The snap fastener 18 is metal and, as well known to thoseskilled in the art, preferably has a coating or plating of silver or thelike composition .to provide a satisfactory electrical interface withthe electrolyte confined in the cavity or chamber 42.

The adhesive layer 20 may be applied .to the lower surface of the sheet12 either before or after assembly. After the parts are assembled andthe adhesive layer 20 applied, a protective waxed paper sheet 44 havinga central cutout 46 forthe cup member 14is applied to the bottom ofthesheet 12. The electrode with the protective sheet 44 may then bestored until ready for use. An alternative arrangement is shown in FIG.4 wherein the cup member 14 is loaded with the electrolyte at the timeof assembly and a suitably formed plastic or paper protective sheet 48is applied in covering relation to both. the lower surface of the sheet12 and the cup member 14 to retain the electrolyte therein. Of course,the protective sheet 44 or the protective sheet 48 are easily removableat the time the electrode 10 is to be used.

As noted above, the metallic snap fastener 18, which is the onlyconductor portion of the electrode 10, should be supported away fromcontact with the skin. The area between the snap fastener 18 and theskin should be completely filled with the electrolyte. Further, themovement of the electrode relative to the skin and the electrolyteshould be positively restricted.

In addition to satisfying these requirements, the electrode 10 of thisinvention has an unusually low profile. These characteristics resultprimarily from the use of the elastic sheet 12 and the design of the cupmember 14.

As apparent from an inspection of FIG. 2, the semicircular or- U-shapedflange 24 forms a convexly curved rim defining the mouth of the cupmember 14 and an outer wall, designated 50, diverging outwardly from therim. The upper margin of the outer wall 50 is substantially coplanarwith 1 the upper surface of the base 26.. The central portion of theelastic sheet is tightly compressed between the confronting basesurfaces of the cup member 14 and the clamp plate 16. Accordingly, priorto attachment of the electrode 10 to the skin, the sheet'12 and itsadhesive layer 20 are axially spaced above the rim of the cup member 14.In order to attach the electrode 10 to theskin, .the sheet 12 must beflexed downwardly, whereupon the annular portion of the sheet 12immediately surrounding the outer wall 50 is stretched to span the areabetween the upper, marginal edge of the diverging outer wall 50 and theportion of the skin to which the adhesive layer 20is secured. Because ofits elastic nature, the stretched portion of the sheet 12 resilientlypresses the convexly curved rim formed by the flange 24 into the skin,creatinga slight depression therein. As a result, the cup member 14 isfirmly retained in sealing relation to the skin, thereby positivelyconfining the electrolyte within the cavity or chamber 42. Also,movement of the cup member 14 and the electrolyte relative to the skinis avoided. The U-shaped flange has a sufficient depth to create aminimal, but adequate spacing between the skin and the conductive lowerplate34' of the snap fastener member 18 within the cavity 42. Becausemovements of the cup member 14 are restricted, the spacing between theplate portion 34 and the skin. is maintained over long periods of use.

For reasons already mentioned, the elastic sheet 12 is preferably formedfrom a foamed or open cell polyvinylchloride havingrelatively closedcell upper and lower surfaces. This type of material can be obtained ata low cost, is sufficiently flexible to conform to the skin, and hassufficient elasticity to press the cup member 14 against the skinwithout tearing or pulling away from,

the skin. As those familiar with such material are aware, the twosurfaces of foamed polyvinylchloride sheets are typically of a slightlydifferent nature, one having a more closed cell construction than theother. Although these surfaces are interchangeable in the manufacture ofthe electrode 10, it is presently preferred that the more open cellsurface be lowermost. The more open cell surface is sufficiently porousto provide for adequate aeration or ventilation of the skin it covers,which is especially important for use over extended periods of time.Also, the more closed cell surface is preferably uppermost because thistype of surface is resistant to soiling.

The various thermoplastic materials mentioned above for use in formingthe cup member 14 and the clamp plate 16 are ideal for this purposebecause they are inexpensive, non-conductive, and can easily be vacuumformed to the desired shape. Although of a flexible nature, athermoplastic sheet is adequately rigid when formed to the illustratedcup shape to prevent collapse of the outer wall 50 under the force ofthe stretched sheet 12. The axial spacing of the rim and the uppermargin of the cup member 14 are thus maintained. A thermoplastic sheetalso has a resiliency which assists in forming a good seal with theparts of the snap fastener member 18. Accordingly, the electrolyte isretained entirely within the chamber 42 and the hollow center of thesnap fastener member 18. Since both the cup member 14 and the clampplate 16 are identically constructed of sheet material, the confrontingmargins of their outer walls compress the elastic sheet 12 therebetween,as indicated at 52. Therefore, substantially the only portion of thesheet 12 which is stretched when applied to. the skin is that portionbetween the outer wall 50 and the skin.

An electrode in accordance with this invention has been made andsuccessfully tested. The electrode had an overall height on the order ofonly 0.3 inch with the depth of the cup member 14 on the order of 0.094inch and the elastic sheet 12 having a thickness of 0.125 inch. Thediameter of the elastic sheet 12 was 2%. inch. The cup member 14, andaccordingly the clamp member 16, had an overall diameter of 0.875 inchwith the diameter of the base 22 being 95 inch. The lower snap fastenerplate 34 had a diameter of 0.406 inch. These dimensions are notcritical. For example, the overall diameter of the cup membercould bebetween approximately 5% inch and one inch with corresponding variationsin the diameter of the cup base 22 and the snap fastener plate 34.Unless the cup member 14 is made deeper, approximately 1 inch is deemedto be the maximum acceptable cup diameter because the skin bounded bythe rim of a larger diameter cup member would likely engage theconductive plate portion 34.

Commercially available medical grade acrylic pressure sensitive adhesivewas applied to the lower surface of the elastic sheet 12 to form theadhesive layer 20. Because the lower surface of the elastic sheet 12 isnot completely impervious, some of the adhesive may have migratedharmlessly beyond the partially closed cell surface. A sufficientlysmall quantity of the adhesive was applied to avoid closing the lowersurface to the passage of air. Of course, the adhesive layer could beobtained in other ways. However, the adhesive layer should be pressuresensitive so that the elastic sheet 12 is stretched as a natural resultof the pressing of the sheet 12 onto the skin. Also, the adhesive layershould not be of such a nature that it adversely affects theskinconforrning flexiblity of the elastic sheet or that it closes thepores of the lower surface of the elastic sheet 12;

The diameter of the illustrated elastic sheet 12 is approximately twoand one-half times the diameter of the cup member 14. It is preferredthat the diameter of the carrier sheet 12 is on the order of two tothree times the diameter of the cup member 14 to provide a broad skincontact area for the pressure sensitive adhesive layer 20. Because thecarrier sheet 12 is flexible. it readily conforms to movements of theskin. Although the cup member 14 is relatively inflexible, it issufficiently firmly held against the skin by the tension in thestretched portion of the carrier sheet 12 that the electrode of thisinvention can be used on subjects engaged in strenuous exercise.

Although a preferred embodiment of this invention has been described, itwill be understood that various changes may be made within the scope ofthe appended claims.

Having thus described my invention, 1 claim:

1. In a medical electrode for attachment to the skin, means defining acollapse resistant cup for an electrolyte, said means including aU-shaped flange forming a convexly curved rim for engagement with theskin and an outer wall having a marginal edge axially spaced from saidrim, an elastic sheet overlying said outer wall and having an adhesiveon its lower surface adjacent said outer wall, means holding a portionof said sheet in engagement with said marginal edge of said outer wallwhereby said sheet may be adhesively secured to the skin by stretchingportions thereof immediately adjacent said outer wall, and whereby saidstretched portions of said sheet resiliently press said outer wall and,accordingly, said rim into engagement with the skin.

2. The electrode of claim 1 wherein said outer wall diverges outwardlyfrom said rim.

3. The electrode of claim 1 wherein said rim and said outer wall arecircular, and wherein said adhesive completely surrounds said outerwall.

4. The electrode of claim 1' wherein said means defining said cupcomprises a thin sheet of plastic formed in the shape of a cavitywasher.

5. In a medical electrode of the type having an inverted, non-conductingand collapse resistant cup member for containing an electrolyte and aconductor located within said cup member remote from its mouth, theimprovement wherein the mouth of said cup member is defined by aU-shaped flange having a convvexly curved rim adapted to engage the skinof a subject, said flange having an outer wall with an upper marginspaced from said rim, and wherein said electrode further includes anelastic sheet overlying and projecting beyond said upper margin, anadhesive on lower surface portions of said elastic sheet beyond saidupper margin for attaching said elastic sheet to the skin, said outerwall supporting said elastic sheet remote from the skin whereby portionsof said elastic sheet immediately adjacent said outer wall are stretchedwhen said elastic sheet is moved into engagement with the skin, thestretched portions of said elastic sheet biasing said rim into firmengagement with the skin.

6. The electrode of claim 5 wherein said adhesive is pressure sensitiveand said elastic sheet is stretched as a result of said elastic sheetbeing pressed against the skin.

7. The electrode of claim 6 wherein said cup member is circular and saidadhesive completely surrounds said cup member.

8. The electrode of claim 5 wherein said cup member is made from a thinsheet of plastic.

9. The electrode of claim 5 further including a clamp plate overlyingsaid elastic sheet and said conductor penetrating said elastic sheet tofix said clamp plate to said cup member thereby to clamp said elasticsheet to said cup member.

10. The electrode of claim 9 wherein said conductor consists ofinterfitting parts pressed together and having upper and lower platesengaging said clamp plate and said cup member, respectively, holdingthem in mutually fixed relation with said elastic sheet clampedtherebetween.

11. The electrode of claim 9 wherein said clamp plate is constructedidentically to said cup member and wherein said clamp plate and said cupmember are aligned on opposite sides of said elastic sheet.

12. The electrode of claim 9 wherein said cup member and said clampplate are both circular and are relatively thin plastic members, saidclamp plate having a margin confronting said upper margin of said cupmember whereby a circular area of said elastic sheet is squeezedtherebetween.

13. The electrode of claim wherein said elastic sheet is made from anopen cell thermoplastic having relatively closed cell upper and lowersurfaces.

14. The electrode of claim 13 wherein said thermoplastic ispolyvinylchloride.

15. In a medical electrode, a low profile non-conducting, relativelyrigid, collapse resistant cup member having a base and a rim, aperturedelastic sheet means connected to said cup member overlying said rim, anadhesive on the lower surface of said sheet means adjacent and insurrounding relation to said rim, a snap fastener projecting throughsaid base and supported. by said base remote from said rim, said snapfastener projecting through an aperture in said sheet means, and aremovable protective cover for said adhesive.

16. The medical electrode of claim 15 wherein said rim has a convexlycurved skin contacting surface.

17. The medical electrode of claim 15 wherein said snap fastener hasinterfitting parts holding said cup member and said sheet means inassembled relation.

Disclaimer 3,696,807.R0man Szpur, Dayton, Ohio. MEDICAL ELECTRODE WITHRELATIVELY RIGID ELECTROLYTE CUP. Patent dated Oct. 10, 1972. Disclaimerfiled Aug. 25, 1983, by the assignee, NDM Corp.

Hereby enters this disclaimer to claims 15 and 17 of said patent.

[Ofiicial Gazette August 13, 1985.]

2. The electrode of claim 1 wherein said outer wall diverges outwardlyfrom said rim.
 3. The electrode of claim 1 wherein said rim and saidouter wall are circular, and wherein said adhesive completely surroundssaid outer wall.
 4. The electrode of claim 1 wherein said means definingsaid cup comprises a thin sheet of plastic formed in the shape of acavity washer.
 5. In a medical electrode of the type having an inverted,non-conducting and collapse resistant cup member for containing anelectrolyte and a conductor located within said cup member remote fromits mouth, the improvement wherein the mouth of said cup member isdefined by a U-shaped flange having a convexly curved rim adapted toengage the skin of a subject, said flange having an outer wall with anupper margin spaced from said rim, and wherein said electrode furtherincludes an elastic sheet overlying and projecting beyond said uppermargin, an adhesive on lower surface portions of said elastic sheetbeyond said upper margin for attaching said elastic sheet to the skin,said outer wall supporting said elastic sheet remote from the skinwhereby portioNs of said elastic sheet immediately adjacent said outerwall are stretched when said elastic sheet is moved into engagement withthe skin, the stretched portions of said elastic sheet biasing said riminto firm engagement with the skin.
 6. The electrode of claim 5 whereinsaid adhesive is pressure sensitive and said elastic sheet is stretchedas a result of said elastic sheet being pressed against the skin.
 7. Theelectrode of claim 6 wherein said cup member is circular and saidadhesive completely surrounds said cup member.
 8. The electrode of claim5 wherein said cup member is made from a thin sheet of plastic.
 9. Theelectrode of claim 5 further including a clamp plate overlying saidelastic sheet and said conductor penetrating said elastic sheet to fixsaid clamp plate to said cup member thereby to clamp said elastic sheetto said cup member.
 10. The electrode of claim 9 wherein said conductorconsists of interfitting parts pressed together and having upper andlower plates engaging said clamp plate and said cup member,respectively, holding them in mutually fixed relation with said elasticsheet clamped therebetween.
 11. The electrode of claim 9 wherein saidclamp plate is constructed identically to said cup member and whereinsaid clamp plate and said cup member are aligned on opposite sides ofsaid elastic sheet.
 12. The electrode of claim 9 wherein said cup memberand said clamp plate are both circular and are relatively thin plasticmembers, said clamp plate having a margin confronting said upper marginof said cup member whereby a circular area of said elastic sheet issqueezed therebetween.
 13. The electrode of claim 5 wherein said elasticsheet is made from an open cell thermoplastic having relatively closedcell upper and lower surfaces.
 14. The electrode of claim 13 whereinsaid thermoplastic is polyvinylchloride.
 15. In a medical electrode, alow profile non-conducting, relatively rigid, collapse resistant cupmember having a base and a rim, apertured elastic sheet means connectedto said cup member overlying said rim, an adhesive on the lower surfaceof said sheet means adjacent and in surrounding relation to said rim, asnap fastener projecting through said base and supported by said baseremote from said rim, said snap fastener projecting through an aperturein said sheet means, and a removable protective cover for said adhesive.16. The medical electrode of claim 15 wherein said rim has a convexlycurved skin contacting surface.
 17. The medical electrode of claim 15wherein said snap fastener has interfitting parts holding said cupmember and said sheet means in assembled relation.